(1) Field of the Invention
The present invention relates to antennas and more particularly to radiators for low-profile, towed submarine antennas.
(2) Description of the Prior Art
Present submarine communication and radio transmission and reception use surface antennas for a variety of requirements including military UHF band (225-400 MHz), LOS, SATCOM, etc. These requirements typically interfere with the covert operation of the submarine. For example, submarine UHF communication is accomplished by using wideband antennas within a mast, which must be extended whenever transmission or reception is required. For communications in coastal waters, raising a mast may compromise the ship's stealth. Furthermore, the current buoyant cable system (with a nominal diameter of 0.65 in.) cannot be used effectively for transmission at these frequencies, because of poor radiation efficiency.
There is a need for an antenna capable of efficient wideband communication while towed horizontally (in a suitably designed container with desirable hydrodynamic properties) in the ocean behind a submarine--a low-profile posture required in order to minimize or eliminate detectability. The term "wideband" is used here to describe an antenna whose input impedance (as described by the voltage standing wave ratio or VSWR) varies within acceptable limits (usually 3 or less) over a large portion (15% or more) of a band that by convention is wide. Moreover, throughout the frequency range of operation, the radiation pattern of the antenna must occupy hemispherical sectors of space above the sea surface that are bounded (roughly) by cones having large included angles in both the azimuth and elevation, to be useful.